[yoannfleurydev]

Closes #28

Summary

Dynamic shell completion with clap_complete's CompleteEnv (COMPLETE=<shell> gitweb) for bash, zsh, fish, elvish and PowerShell. Besides the options, it suggests values read from the current repository:

 main
+  CompleteEnv::with_factory(Opt::command).complete()   # answers COMPLETE=<shell>, then exits
   Opt::parse()
   run(opt)

 Opt
-  --branch
+  --branch  -> git::get_branches   # local + remote-tracking (prefix stripped), deduped, sorted, no HEAD
-  --tag
+  --tag     -> git::get_tags
-  --remote
+  --remote  -> git::get_remotes

Outside a repository, or on any git error, a completer returns nothing and prints nothing.

The issue suggested generating scripts in GitHub Actions. With dynamic completion, the generated script is only a stub that calls back into the binary, so the README tells users to source it at shell startup instead. The stub then stays in sync across upgrades.

Evidence

• Before: gitweb -b <TAB> offers nothing (there's no completion at all).
  After: fish, with COMPLETE=fish ./target/debug/gitweb | source loaded, in this repo:

  $ complete -C "gitweb -b "
  ci/improve-actions
  dependabot/cargo/thiserror-2.0.21     # remote-only, origin/ stripped
  feat/update-dependencies
  main                                  # local + origin/main merged, origin/HEAD dropped
  yoannfleurydev/autocomplete-on-tab
  $ complete -C "gitweb -t v0.3"
  v0.3.0 … v0.3.5
  $ complete -C "gitweb -r "
  origin
  $ cd /tmp; complete -C "gitweb -b "
  (nothing)
  

  I also drove the zsh and bash protocols directly and got the same candidates.

• New tests: git::tests builds a throwaway repo (local branch, remote-tracking branches, origin/HEAD, tags, two remotes) and checks the three helpers. options::tests runs Opt::command().debug_assert(). cargo test: 17 passed. cargo clippy --all-features: no new warnings.

Merge Danger

Door: two-way

The only lasting commitment is the COMPLETE variable name, which Homebrew's shell_parameter_format: :clap expects.

Blast Radius: small

• CompleteEnv only takes over when COMPLETE is set to a known shell name. Otherwise gitweb runs as before.
• clap_complete is pinned to =4.6.11 because dynamic completion is behind the unstable-dynamic feature and cargo install gitweb ignores Cargo.lock. Dependabot bumps will need a manual look.
• clap now requires 4.6 (needed by clap_complete). The lockfile was already on 4.6.7.

Follow-up after release: update the homebrew-gitweb formula to use generate_completions_from_executable(bin/"gitweb", shell_parameter_format: :clap).

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